1. Field of the Invention
The present invention relates in general to a shift-register circuit. In particular, the present invention relates to a bi-directional shift-register circuit for driving a liquid crystal display.
2. Description of the Related Art
A frame of a liquid crystal display (LCD) is generated by a plurality of pixels arranged in an array. Sequential pulses are basic signals for driving the LCD. Sequential pulses are generated by a shift-register circuit, thus, the shift register circuit is a general unit for driving an LCD circuit.
A single scanning turn along one direction, however, does not satisfy all requirements of an LCD product. For example, some digital camera displays are rotated according to the placement angle of the camera. Additionally, some LCD monitors included a monitor rotating function hence LCD displays capable of multiple scanning turns are required. Thus, a shift-register circuit with multiple signal output turns is also required.
In addition, the power consumption of a transmission line is proportional to the amplitude of the signal thereon.
The power loss of the transmission line is obtained as follow:
P=fcv2; 
wherein P is power loss of the transmission line, f is a frequency, c is a parasitic capacitance of the transmission line, and v is the voltage difference of a clock signal.
Therefore, the conventional shift-register circuit requires a relatively high voltage clock supply, which induces high power consumption.
The object of the present invention is to provide a bi-directional shift-register circuit capable of operating with a low-voltage clock signal supply to reduce power consumption required by clock signal transmission.
According to the above-mentioned objects, the present invention provides a bi-directional shift-register circuit for outputting data in different turns according to a low-voltage clock signal, a first directional signal, and a second directional signal. The bi-directional shift-register circuit comprises a plurality of shift-register units coupled to a first bi-directional control circuit. Each shift-register unit has a level shifter and an input, an output terminal and a clock input terminal for receiving the low-voltage clock signal. The first bi-directional control circuit is coupled to the first-stage output terminal, the third-stage output terminal and the first directional signal or second directional signal, wherein the first bi-directional control circuit outputs the signal of the first-stage output terminal to the second-stage input terminal when the first bi-directional control circuit receives the first directional signal, and outputs the signal of the third-stage output terminal to the second-stage input terminal when the first bi-directional control circuit receives the second directional signal.
In addition, the present invention provides another bi-directional shift-register circuit comprising thin film transistors for outputting data in different turns according to a low-voltage clock signal, a first directional signal, and a second directional signal. The bi-directional shift-register circuit comprises a plurality of shift-register units that is coupled to a first bi-directional control circuit. Each of the shift-register units has a level shifter and an input, an output terminal and a clock input terminal for receiving the low-voltage clock signal. The first bi-directional control circuit is coupled to the first-stage output terminal, the third-stage output terminal and the first directional signal or second directional signal, wherein the first bi-directional control circuit outputs the signal of the first-stage output terminal to the second-stage first input terminal and outputs the signal of the third-stage output terminal to the second-stage second input terminal when the first bi-directional control circuit receives the first directional signal, and outputs the signal of the third-stage output terminal to the second-stage first input terminal and outputs the signal of the first-stage output terminal to the second-stage second input terminal when the first bi-directional control circuit receives the second directional signal.